The present invention relates to an actuator module for inducing the relative motion of robot members joined in a robot joint, and a robot using the actuator module. In particular, the invention relates to an actuator module comprising a Ferguson epicyclic gear train, integral motor and integrated control means (brakes, encoders, sensors, etc.).
Today's robots are designed with virtually no standardization. This results in a costly technology which cannot rapidly adapt to emerging technologies and may be obsolete before it goes to production. Modularity would do much to reduce the level of cost and would reduce the threat of obsolescence, allowing rapid changeover in favor of improved module technology. The model of the personal computer can provide a benchmark for the benefits of modularity in another system architecture. While the original computers were dedicated mainframes, each designed separately with little compatibility from one generation to the next, the personal computer is now highly modular, layered, interfaced at each level, etc. in a nearly standardized format.
The pressing need is to develop a robot architecture which can rapidly evolve in the same fashion as is now feasible for personal computers. Existing drive systems usually include encoders, brakes, motors, drive trains and joint bearings, each provided with its own housing, mounting plates, wiring interfaces, etc. Before the present invention, no thought had been given to aggressively integrating these multi-component systems into a combined whole to reduce weight, size and complexity and to increase scalability and adaptability. The architecture which results from modularity maximizes the number of physical parameters still available so that a designer has a full selection with which to design.
Of course, there are literally billions of systems which can be derived from the hundreds of design parameters available. Hence, a strategy for design must be developed which allows optimum results to occur in smaller, more addressable packages. This is the primary design argument in favor of modularity in robotics. Evolutionary changes in previous designs are presently made without having the capability to make dramatic changes which could provide substantial benefits.
Although the need for modularity and compactness has been recognized in the prior art, see, e.g., U.S. Pat. Nos. 4,738,576 and 4,062,601, these proposed solutions retain such deficiencies as separately housed motors and unnecessary complexity.
The use of epicyclic gear trains is also known in the art. See, e.g., U.S. Pat. Nos. 4,686,402; 4,492,510; and Nasa Publication JSC-09709 (June 1975). These devices are particularly suited for robotics because of their compactness (for the reduction ratios possible), efficiency (and thus back-driveability), durability and smooth operation. As with most gear trains, however, the use of an epicyclic gear train typically adds a relatively heavy structure to the robot joint assembly. The prior art, characterized by separately-housed, discrete components and long force paths, has not provided an adequate solution to this and other stumbling blocks facing the development of robot-drive technology. Finally, none of the proposed solutions combine modularity and compactness with superior redundancy and stiffness characteristics.